The present invention relates to a data receiving apparatus which reproduces and outputs multimedia data such as images and characters transmitted from, for example, a computer network and a digital broadcasting network, or multimedia data such as images and characters outputted from drives of information media such as CD-ROM and DVD to a personal computer and a television receiver, and more specifically, relates to a data receiving apparatus which has a function to protect decrypted data transmitted or outputted with being encrypted.
This application is based on Japanese Patent Application No. 8-233100, filed Sep. 3, 1996, No. 8-300407, filed Nov. 12, 1996, No. 9-112539, filed Apr. 30, 1997, and No. 9-112540, filed Apr. 30, 1997, the content of which is incorporated herein by reference.
In recent years, there have been proposed a data receiving apparatus which receives so-called multimedia data transmitted from digital broadcasting networks such as a computer network and digital satellite broadcasting, and from data storage media such as DVD (Digital Versatile Disc), and which outputs them into a personal computer and a television receiver. When each home is equipped with such a data receiving apparatus, a service providing system of multimedia data including a video, sound and characters such as video-on-demand service can be realized.
Consequently, where the above-mentioned service providing system is constructed, it is important to protect rights such as a copyright of creators and data providers (individual and companies) of multimedia data. Since multimedia data are provided as digital data, it is easy to copy the data by using a personal computer. Moreover, where multimedia data are converted into an analog signal (video signal, etc.) so as to be supplied to a television receiver, it is easy to record the data into a video tape by a video cassette recorder. Therefore, where a system which distributes multimedia data efficiently is constructed, the problem of protecting rights of data providers is inevitable and important matter.
In general, in order to prevent a third party who is not a genuine contractor from receiving data without fee, a service provider provides encrypted data. The service provider informs only the contractors of encryption keys so that only the contractors can decrypt the encrypted data correctly. Here, data are supplied to the contractors through not only a cable network but also a wireless LAN, television broadcasting, a storage medium, etc.
As a conventional example of such a data receiving apparatus, there is an apparatus shown in FIG. 1. This apparatus comprises a set top unit 10, a security module 20 and an IC card 30, but the set top unit 10 and the security module 20 form one unit actually, and thus one product (information receiving apparatus) is realized. Therefore, only IC card 30 is separated from this product.
In the case of a network, wireless LAN or television broadcasting, encrypted data (here, encrypt means scramble, and hereinafter, encrypted data is referred to as scrambled data) supplied from an antenna or outputted from a storage medium are inputted into a receiver/demodulator 12 of the set top unit 10. In this example, original data is digital image data which have been encoded by the MPEG encoding algorithm. Output of the receiver/demodulator 12 (scrambled data) is supplied to the security module 20, and is inputted to a descramble circuit 22 and a filter 24.
The filter 24 extracts ECM data and EMM data from inputted stream data, and supplies them to an interface 26. The ECM and EMM data are data which are defined in the MPEG-2, and ECM means Entitlement Control Message, and EMM means Entitlement Management Message. Concretely, they are a stream including control data which flows in an MPEG transport stream when payload of a packet of the MPEG transport stream which transports an image and sound data is scrambled.
The ECM includes data for access control which is peculiar to the streams of image and sound data such as a key necessary for releasing the scramble, a program number (in the MPEG-2, the program means a group of image and sound stream data having a common time base), and the fee for the program.
The EMM includes data for access control relating to the whole system. For example, the EMM includes names of new users and new program numbers.
In such a manner, the filter 24 performs filtering for extracting the streams (in the case of a program stream, a program stream map, and in the case of a transport stream, a TS program map section) including ECM and EMM transmitted mixing with the streams of the image and sound data encoded by the MPEG encoding algorithm. Such filtering is performed according to PIDs (packet ID) allocated to the packets and values of stream IDs.
The interface 26 is connected to the IC card 30 owned by a contractor. The service provider who transmits digital image data previously writes a descramble key corresponding to scramble of transmission, a password of an user, etc. into the IC card 30, and hands it to the user upon the contraction.
In the system shown in FIG. 1 owning the data receiving apparatus (formed of the set top unit 10 and the security module 20) means a sort of authentication, but in order to cope with an apparatus theft, authentication such as password verification is actually performed.
For this reason, the IC card 30 is connected to the interface 26, the authentication is performed by using a user's password which has been previously written into the IC card 30. When the authentication is finished successfully, the descramble key or secret data required for decrypting encrypted descramble key is inputted from the IC card 30 into the descramble circuit 22 in the security module 20.
The descramble circuit 22 descrambles scrambled data supplied from the set top unit 10 by using the descramble key, and transmits the original digital image data coded by the MPEG method back to the set top unit 10. The original image data are outputted through a demultiplexer 14 and an MPEG decoder 16 in the set top unit 10 into a user terminal (image display unit, etc.), not shown. The MPEG decoder 16 includes an analog/digital converter, and outputs an analog video signal corresponding to the original image data.
In such a manner, the scrambled data are descrambled according to the security module 20, and the original digital image data coded by the MPEG method are supplied to the set top unit 10. Therefore, only a genuine user having the descramble key in the IC card 30 can descramble the scrambled data.
However, in the data receiving apparatus, the user's secret information such as the descramble key and the password appears in the interface 26. Therefore, the user's secret information can be stolen by a third party through the interface 26, and thus there arises problems of the user protection and security.
In order to avoid such a problem, there is proposed that the IC card 30 and the security module 20 form one unit (the set top unit 10 is separated from the security module 20). In this case, user's secret information is not stolen by a third party, but since original digital image data, which have been descrambled, appears at the interface between the security module 20 and the set top unit 10, the digital data can be utilized (copied, etc.) illegally, and this threatens the service provider.
The above-mentioned problems are not limited to the case of receiving and decrypting data supplied through a network, so the problems arise similarly in the case of distribution of packaged software etc.
As described above, the conventional data receiving apparatus was insufficient to protect encrypted data.